1. Technical Field
The present disclosure relates to a system and method for recycling sterilant gas. In particular, the present disclosure is directed to recovery and reuse of high concentration flammable sterilant gas mixtures, wherein the sterilant gas mixture is in concentrations greater than 20% by volume to a near an undiluted state of 100% by volume.
2. Discussion of Related Art
Ethylene oxide (“ETO”) is a sterilizing agent well known for its effectiveness at certain gas concentrations. The objects which are to be sterilized are placed in a hermitically sealed sterilization chamber and the ETO vapor is pumped into the chamber. ETO gas is extremely flammable even in the absence of air and is, therefore, used with extreme caution in high concentrations at low pressures for sterilization purposes. Presently, high concentration ETO gas is not recycled and is only used once, afterwards the gas is then discharged to an emission control device for destruction.
One method for reusing ETO gas involves the use of a low concentration mixture of ETO and an inert gas at higher process pressures. High process pressures (e.g., up to 4 atmospheres) allow an increase in the ETO gas concentration to an acceptable milligram per liter value for effective sterilization. Mixtures having ratios of ETO to inert gas of 10/90 and 20/80 are generally used. These mixtures contain sufficient ETO concentration to assure sterilization regardless of the material being sterilized under normal temperature and at above atmospheric pressure conditions. Relative non-flammability of diluted ETO and inert gas mixtures allows for recycling of these mixtures. However, these mixtures are not as effective as higher concentrations of ETO gas.
The concentration of ETO decreases with continual use during the sterilization process since ETO is consumed in reaction with bacteria, water vapor, alcohol and the like during the sterilization process. It is possible for the ETO gas concentration to be consumed to an unsatisfactory concentration for consistent sterilization effect. Therefore, low concentration gas mixtures require processing using higher pressure rated vessels, which are more expensive. This process also involves processing the gases at above atmospheric pressures and, therefore, carries the risk of fugitive and catastrophic leakage. Consequently, in the industry today, all large ETO sterilizer chambers are designed to operate using low pressure and high concentration ETO gas. Existing sterilizers in use in the industry are not rated for the higher pressures that are required to recycle low concentration ETO gas sterilants.
It is desirable to provide a system and method for recycling sterilant gas mixtures having near 100% concentration of ETO gas to obtain maximum sterilization effectiveness while minimizing the complexity of the process and the cost of the sterilization equipment. It is desirable to provide a system that can be retrofitted to existing sterilization facilities, by the utilization of the existing sterilization process equipment and avoiding the expenses that are associated with complete system replacement.